Recently, the development of the backbone network communication line as mainly focusing on the optical fiber communication technology is proceeding steadily, in such a situation, the electric wirings in the information terminal are becoming a bottleneck. Against such background, instead of the conventional electric circuit substrate in which all signal transmissions are made by using the electric signal, the optoelectronic composite substrate (optical waveguide device) of the type that transmits high-speed parts by the light signal has been proposed, in order to compensate the limit of transmission speed of the electric signal.
In the case that the light emitting element and the light receiving element of the surface mounted type are mounted to the optical waveguide, the light path conversion inclined surface that is inclined to intersect with the light propagation direction at an angle of 45° is formed at both ends of the optical waveguide, and then the light path conversion mirror is constructed to contact the light path conversion inclined surface, so that the light path conversion is made.
In Patent Literature 1 (Japanese Laid-open Patent Publication No. 2002-365457), it is set forth that the closed space (the air space, or the like) that is enclosed by the light path conversion inclined surface of the optical waveguide and the substrate is used as the light path conversion mirror.
Also, in Patent Literature 2 (Japanese Laid-open Patent Publication No. 2008-250007), it is set forth that the metal film is formed on the light path conversion inclined surface of the optical waveguide by a deposition, or the like, and is used as the light path conversion mirror.
In Patent Literature 3 (Japanese Laid-open Patent Publication No. 2008-134621), it is set forth that the solder resist film of high reflectance is formed on the printed-wiring board by using a white light-curing/thermosetting resin composition.
In the case where a light reflection is caused by utilizing the space (the air space, or the like)(Patent Literature 1), the space that contacts the light path conversion inclined surface of the optical waveguide must be provided. Therefore, it is feared that a structure of the substrate becomes complicated to bring about an increase in cost.
Also, in the case where a light reflection is caused by forming the metal film on the light path conversion inclined surface of the optical waveguide (Patent Literature 2), it is needed to form the metal film by the vacuum deposition or the sputter method. Therefore, the new production facilities must be introduced into the mounting line, and it is feared that such situation is at a disadvantage in cost.